1. Field of the Invention
The invention relates to a drive circuit for a power MOSFET having a load connected between its source electrode and ground potential and an electronic switch connected between its gate electrode and ground potential.
2. Description of the Prior Art
Such a drive circuit has been described, for example, in the German journal "Elektronik Industrie" 4-1985, pages 32 to 38. It comprises a plurality of electronic components which carry out logic operations and switching functions. The output of the electronic switch is connected to the gate electrode of a power MOSFET and the source electrode of the power MOSFET is in series with a load. The side of the load remote from the MOSFET is grounded. The electronic switch itself is also grounded.
In many cases, e.g. in the electric systems of motor vehicles, the ground terminal to which the electronic switch is connected is not identical with the ground terminal to which the load is connected. Now, if due to vibrations or corrosion for example, an interruption occurs between ground potential and the terminal of the electronic switch intended for connection to ground potential, the output potential of the switch changes. In turn, the gate potential of the power MOSFET will change and it may be partially switched on. A considerable power dissipation will then occur in the power MOSFET.